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href="/fe/vue/slot.html" class="sidebar-link">面试官：说说你对slot的理解？slot使用场景有哪些？</a></li><li><a href="/fe/vue/observable.html" class="sidebar-link">面试官：Vue.observable你有了解过吗？说说看</a></li><li><a href="/fe/vue/key.html" class="sidebar-link">Key的理解</a></li><li><a href="/fe/vue/keepalive.html" class="sidebar-link">面试官：说说你对keep-alive的理解是什么？</a></li><li><a href="/fe/vue/modifier.html" class="sidebar-link">面试官：Vue常用的修饰符有哪些有什么应用场景</a></li><li><a href="/fe/vue/directive.html" class="sidebar-link">面试官：你有写过自定义指令吗？自定义指令的应用场景有哪些？</a></li><li><a href="/fe/vue/filter.html" class="sidebar-link">面试官：Vue中的过滤器了解吗？过滤器的应用场景有哪些？</a></li><li><a href="/fe/vue/vnode.html" class="sidebar-link">虚拟DOM</a></li><li><a href="/fe/vue/diff.html" class="sidebar-link">Diff 算法</a></li><li><a href="/fe/vue/axios.html" class="sidebar-link">面试官：Vue项目中有封装过axios吗？主要是封装哪方面的？</a></li><li><a href="/fe/vue/axios_code.html" class="sidebar-link">面试官：你了解axios的原理吗？有看过它的源码吗？</a></li><li><a href="/fe/vue/ssr.html" class="sidebar-link">面试官：SSR解决了什么问题？有做过SSR吗？你是怎么做的？</a></li><li><a href="/fe/vue/structure.html" class="sidebar-link">面试官：说下你的vue项目的目录结构，如果是大型项目你该怎么划分结构和划分组件呢？</a></li><li><a href="/fe/vue/permission.html" class="sidebar-link">面试官：vue要做权限管理该怎么做？如果控制到按钮级别的权限怎么做？</a></li><li><a href="/fe/vue/cors.html" class="sidebar-link">面试官：Vue项目中你是如何解决跨域的呢？</a></li><li><a href="/fe/vue/404.html" class="sidebar-link">面试官：vue项目本地开发完成后部署到服务器后报404是什么原因呢？</a></li><li><a href="/fe/vue/error.html" class="sidebar-link">面试官：你是怎么处理vue项目中的错误的？</a></li><li><a href="/fe/vue/vue_router.html" class="sidebar-link">Vue Router</a></li><li><a href="/fe/vue/vue-debounce-throttle.html" class="sidebar-link">vue防抖调研</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue3</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="面试官-vue实例挂载的过程"><a href="#面试官-vue实例挂载的过程" class="header-anchor">#</a> 面试官：Vue实例挂载的过程</h1> <p><img src="https://static.vue-js.com/63194810-3a09-11eb-85f6-6fac77c0c9b3.png" alt=""></p> <h2 id="一、思考"><a href="#一、思考" class="header-anchor">#</a> 一、思考</h2> <p>我们都听过知其然知其所以然这句话</p> <p>那么不知道大家是否思考过<code>new Vue()</code>这个过程中究竟做了些什么？</p> <p>过程中是如何完成数据的绑定，又是如何将数据渲染到视图的等等</p> <h2 id="一、分析"><a href="#一、分析" class="header-anchor">#</a> 一、分析</h2> <p>首先找到<code>vue</code>的构造函数</p> <p>源码位置：src\core\instance\index.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">Vue</span> <span class="token punctuation">(</span><span class="token parameter">options</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span>
    <span class="token operator">!</span><span class="token punctuation">(</span><span class="token keyword">this</span> <span class="token keyword">instanceof</span> <span class="token class-name">Vue</span><span class="token punctuation">)</span>
  <span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">warn</span><span class="token punctuation">(</span><span class="token string">'Vue is a constructor and should be called with the `new` keyword'</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">_init</span><span class="token punctuation">(</span>options<span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p><code>options</code>是用户传递过来的配置项，如<code>data、methods</code>等常用的方法</p> <p><code>vue</code>构建函数调用<code>_init</code>方法，但我们发现本文件中并没有此方法，但仔细可以看到文件下方定定义了很多初始化方法</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">initMixin</span><span class="token punctuation">(</span>Vue<span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token comment">// 定义 _init</span>
<span class="token function">stateMixin</span><span class="token punctuation">(</span>Vue<span class="token punctuation">)</span><span class="token punctuation">;</span>    <span class="token comment">// 定义 $set $get $delete $watch 等</span>
<span class="token function">eventsMixin</span><span class="token punctuation">(</span>Vue<span class="token punctuation">)</span><span class="token punctuation">;</span>   <span class="token comment">// 定义事件  $on  $once $off $emit</span>
<span class="token function">lifecycleMixin</span><span class="token punctuation">(</span>Vue<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">// 定义 _update  $forceUpdate  $destroy</span>
<span class="token function">renderMixin</span><span class="token punctuation">(</span>Vue<span class="token punctuation">)</span><span class="token punctuation">;</span>   <span class="token comment">// 定义 _render 返回虚拟dom</span>
</code></pre></div><p>首先可以看<code>initMixin</code>方法，发现该方法在<code>Vue</code>原型上定义了<code>_init</code>方法</p> <p>源码位置：src\core\instance\init.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token class-name">Vue</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">_init</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">options<span class="token operator">?</span><span class="token operator">:</span> Object</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">const</span> vm<span class="token operator">:</span> Component <span class="token operator">=</span> <span class="token keyword">this</span>
    <span class="token comment">// a uid</span>
    vm<span class="token punctuation">.</span>_uid <span class="token operator">=</span> uid<span class="token operator">++</span>
    <span class="token keyword">let</span> startTag<span class="token punctuation">,</span> endTag
    <span class="token comment">/* istanbul ignore if */</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> config<span class="token punctuation">.</span>performance <span class="token operator">&amp;&amp;</span> mark<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      startTag <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue-perf-start:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>vm<span class="token punctuation">.</span>_uid<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span>
      endTag <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue-perf-end:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>vm<span class="token punctuation">.</span>_uid<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span>
      <span class="token function">mark</span><span class="token punctuation">(</span>startTag<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">// a flag to avoid this being observed</span>
    vm<span class="token punctuation">.</span>_isVue <span class="token operator">=</span> <span class="token boolean">true</span>
    <span class="token comment">// merge options</span>
    <span class="token comment">// 合并属性，判断初始化的是否是组件，这里合并主要是 mixins 或 extends 的方法</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>options <span class="token operator">&amp;&amp;</span> options<span class="token punctuation">.</span>_isComponent<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">// optimize internal component instantiation</span>
      <span class="token comment">// since dynamic options merging is pretty slow, and none of the</span>
      <span class="token comment">// internal component options needs special treatment.</span>
      <span class="token function">initInternalComponent</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> options<span class="token punctuation">)</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span> <span class="token comment">// 合并vue属性</span>
      vm<span class="token punctuation">.</span>$options <span class="token operator">=</span> <span class="token function">mergeOptions</span><span class="token punctuation">(</span>
        <span class="token function">resolveConstructorOptions</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span>constructor<span class="token punctuation">)</span><span class="token punctuation">,</span>
        options <span class="token operator">||</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
        vm
      <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    <span class="token comment">/* istanbul ignore else */</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">// 初始化proxy拦截器</span>
      <span class="token function">initProxy</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
      vm<span class="token punctuation">.</span>_renderProxy <span class="token operator">=</span> vm
    <span class="token punctuation">}</span>
    <span class="token comment">// expose real self</span>
    vm<span class="token punctuation">.</span>_self <span class="token operator">=</span> vm
    <span class="token comment">// 初始化组件生命周期标志位</span>
    <span class="token function">initLifecycle</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span>
    <span class="token comment">// 初始化组件事件侦听</span>
    <span class="token function">initEvents</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span>
    <span class="token comment">// 初始化渲染方法</span>
    <span class="token function">initRender</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span>
    <span class="token function">callHook</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> <span class="token string">'beforeCreate'</span><span class="token punctuation">)</span>
    <span class="token comment">// 初始化依赖注入内容，在初始化data、props之前</span>
    <span class="token function">initInjections</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span> <span class="token comment">// resolve injections before data/props</span>
    <span class="token comment">// 初始化props/data/method/watch/methods</span>
    <span class="token function">initState</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span>
    <span class="token function">initProvide</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span> <span class="token comment">// resolve provide after data/props</span>
    <span class="token function">callHook</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> <span class="token string">'created'</span><span class="token punctuation">)</span>

    <span class="token comment">/* istanbul ignore if */</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> config<span class="token punctuation">.</span>performance <span class="token operator">&amp;&amp;</span> mark<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      vm<span class="token punctuation">.</span>_name <span class="token operator">=</span> <span class="token function">formatComponentName</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">)</span>
      <span class="token function">mark</span><span class="token punctuation">(</span>endTag<span class="token punctuation">)</span>
      <span class="token function">measure</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>vm<span class="token punctuation">.</span>_name<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> init</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> startTag<span class="token punctuation">,</span> endTag<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    <span class="token comment">// 挂载元素</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>el<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      vm<span class="token punctuation">.</span><span class="token function">$mount</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>el<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
</code></pre></div><p>仔细阅读上面的代码，我们得到以下结论：</p> <ul><li><p>在调用<code>beforeCreate</code>之前，数据初始化并未完成，像<code>data</code>、<code>props</code>这些属性无法访问到</p></li> <li><p>到了<code>created</code>的时候，数据已经初始化完成，能够访问<code>data</code>、<code>props</code>这些属性，但这时候并未完成<code>dom</code>的挂载，因此无法访问到<code>dom</code>元素</p></li> <li><p>挂载方法是调用<code>vm.$mount</code>方法</p></li></ul> <p><code>initState</code>方法是完成<code>props/data/method/watch/methods</code>的初始化</p> <p>源码位置：src\core\instance\state.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">initState</span> <span class="token punctuation">(</span><span class="token parameter">vm<span class="token operator">:</span> Component</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token comment">// 初始化组件的watcher列表</span>
  vm<span class="token punctuation">.</span>_watchers <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
  <span class="token keyword">const</span> opts <span class="token operator">=</span> vm<span class="token punctuation">.</span>$options
  <span class="token comment">// 初始化props</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>opts<span class="token punctuation">.</span>props<span class="token punctuation">)</span> <span class="token function">initProps</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> opts<span class="token punctuation">.</span>props<span class="token punctuation">)</span>
  <span class="token comment">// 初始化methods方法</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>opts<span class="token punctuation">.</span>methods<span class="token punctuation">)</span> <span class="token function">initMethods</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> opts<span class="token punctuation">.</span>methods<span class="token punctuation">)</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>opts<span class="token punctuation">.</span>data<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token comment">// 初始化data  </span>
    <span class="token function">initData</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token function">observe</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span>_data <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token boolean">true</span> <span class="token comment">/* asRootData */</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>opts<span class="token punctuation">.</span>computed<span class="token punctuation">)</span> <span class="token function">initComputed</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> opts<span class="token punctuation">.</span>computed<span class="token punctuation">)</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>opts<span class="token punctuation">.</span>watch <span class="token operator">&amp;&amp;</span> opts<span class="token punctuation">.</span>watch <span class="token operator">!==</span> nativeWatch<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">initWatch</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> opts<span class="token punctuation">.</span>watch<span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>我们和这里主要看初始化<code>data</code>的方法为<code>initData</code>，它与<code>initState</code>在同一文件上</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">initData</span> <span class="token punctuation">(</span><span class="token parameter">vm<span class="token operator">:</span> Component</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">let</span> data <span class="token operator">=</span> vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>data
  <span class="token comment">// 获取到组件上的data</span>
  data <span class="token operator">=</span> vm<span class="token punctuation">.</span>_data <span class="token operator">=</span> <span class="token keyword">typeof</span> data <span class="token operator">===</span> <span class="token string">'function'</span>
    <span class="token operator">?</span> <span class="token function">getData</span><span class="token punctuation">(</span>data<span class="token punctuation">,</span> vm<span class="token punctuation">)</span>
    <span class="token operator">:</span> data <span class="token operator">||</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">isPlainObject</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    data <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> <span class="token function">warn</span><span class="token punctuation">(</span>
      <span class="token string">'data functions should return an object:\n'</span> <span class="token operator">+</span>
      <span class="token string">'https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function'</span><span class="token punctuation">,</span>
      vm
    <span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
  <span class="token comment">// proxy data on instance</span>
  <span class="token keyword">const</span> keys <span class="token operator">=</span> Object<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span>
  <span class="token keyword">const</span> props <span class="token operator">=</span> vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>props
  <span class="token keyword">const</span> methods <span class="token operator">=</span> vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>methods
  <span class="token keyword">let</span> i <span class="token operator">=</span> keys<span class="token punctuation">.</span>length
  <span class="token keyword">while</span> <span class="token punctuation">(</span>i<span class="token operator">--</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">const</span> key <span class="token operator">=</span> keys<span class="token punctuation">[</span>i<span class="token punctuation">]</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">// 属性名不能与方法名重复</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span>methods <span class="token operator">&amp;&amp;</span> <span class="token function">hasOwn</span><span class="token punctuation">(</span>methods<span class="token punctuation">,</span> key<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">warn</span><span class="token punctuation">(</span>
          <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">Method &quot;</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">&quot; has already been defined as a data property.</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span>
          vm
        <span class="token punctuation">)</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
    <span class="token comment">// 属性名不能与state名称重复</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>props <span class="token operator">&amp;&amp;</span> <span class="token function">hasOwn</span><span class="token punctuation">(</span>props<span class="token punctuation">,</span> key<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> <span class="token function">warn</span><span class="token punctuation">(</span>
        <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">The data property &quot;</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">&quot; is already declared as a prop. </span><span class="token template-punctuation string">`</span></span> <span class="token operator">+</span>
        <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">Use prop default value instead.</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span>
        vm
      <span class="token punctuation">)</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">isReserved</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 验证key值的合法性</span>
      <span class="token comment">// 将_data中的数据挂载到组件vm上,这样就可以通过this.xxx访问到组件上的数据</span>
      <span class="token function">proxy</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">_data</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> key<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
  <span class="token comment">// observe data</span>
  <span class="token comment">// 响应式监听data是数据的变化</span>
  <span class="token function">observe</span><span class="token punctuation">(</span>data<span class="token punctuation">,</span> <span class="token boolean">true</span> <span class="token comment">/* asRootData */</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>仔细阅读上面的代码，我们可以得到以下结论：</p> <ul><li><p>初始化顺序：<code>props</code>、<code>methods</code>、<code>data</code></p></li> <li><p><code>data</code>定义的时候可选择函数形式或者对象形式（组件只能为函数形式）</p></li></ul> <p>关于数据响应式在这就不展开详细说明</p> <p>上文提到挂载方法是调用<code>vm.$mount</code>方法</p> <p>源码位置：</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token class-name">Vue</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">$mount</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span>
  <span class="token parameter">el<span class="token operator">?</span><span class="token operator">:</span> string <span class="token operator">|</span> Element<span class="token punctuation">,</span>
  hydrating<span class="token operator">?</span><span class="token operator">:</span> boolean</span>
<span class="token punctuation">)</span><span class="token operator">:</span> Component <span class="token punctuation">{</span>
  <span class="token comment">// 获取或查询元素</span>
  el <span class="token operator">=</span> el <span class="token operator">&amp;&amp;</span> <span class="token function">query</span><span class="token punctuation">(</span>el<span class="token punctuation">)</span>

  <span class="token comment">/* istanbul ignore if */</span>
  <span class="token comment">// vue 不允许直接挂载到body或页面文档上</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>el <span class="token operator">===</span> document<span class="token punctuation">.</span>body <span class="token operator">||</span> el <span class="token operator">===</span> document<span class="token punctuation">.</span>documentElement<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> <span class="token function">warn</span><span class="token punctuation">(</span>
      <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">Do not mount Vue to &lt;html&gt; or &lt;body&gt; - mount to normal elements instead.</span><span class="token template-punctuation string">`</span></span>
    <span class="token punctuation">)</span>
    <span class="token keyword">return</span> <span class="token keyword">this</span>
  <span class="token punctuation">}</span>

  <span class="token keyword">const</span> options <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>$options
  <span class="token comment">// resolve template/el and convert to render function</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>options<span class="token punctuation">.</span>render<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">let</span> template <span class="token operator">=</span> options<span class="token punctuation">.</span>template
    <span class="token comment">// 存在template模板，解析vue模板文件</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>template<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> template <span class="token operator">===</span> <span class="token string">'string'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>template<span class="token punctuation">.</span><span class="token function">charAt</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token string">'#'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
          template <span class="token operator">=</span> <span class="token function">idToTemplate</span><span class="token punctuation">(</span>template<span class="token punctuation">)</span>
          <span class="token comment">/* istanbul ignore if */</span>
          <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> <span class="token operator">!</span>template<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token function">warn</span><span class="token punctuation">(</span>
              <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">Template element not found or is empty: </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>options<span class="token punctuation">.</span>template<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span>
              <span class="token keyword">this</span>
            <span class="token punctuation">)</span>
          <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
      <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>template<span class="token punctuation">.</span>nodeType<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        template <span class="token operator">=</span> template<span class="token punctuation">.</span>innerHTML
      <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
          <span class="token function">warn</span><span class="token punctuation">(</span><span class="token string">'invalid template option:'</span> <span class="token operator">+</span> template<span class="token punctuation">,</span> <span class="token keyword">this</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>el<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">// 通过选择器获取元素内容</span>
      template <span class="token operator">=</span> <span class="token function">getOuterHTML</span><span class="token punctuation">(</span>el<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>template<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">/* istanbul ignore if */</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> config<span class="token punctuation">.</span>performance <span class="token operator">&amp;&amp;</span> mark<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">mark</span><span class="token punctuation">(</span><span class="token string">'compile'</span><span class="token punctuation">)</span>
      <span class="token punctuation">}</span>
      <span class="token comment">/**
       *  1.将temmplate解析ast tree
       *  2.将ast tree转换成render语法字符串
       *  3.生成render方法
       */</span>
      <span class="token keyword">const</span> <span class="token punctuation">{</span> render<span class="token punctuation">,</span> staticRenderFns <span class="token punctuation">}</span> <span class="token operator">=</span> <span class="token function">compileToFunctions</span><span class="token punctuation">(</span>template<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        outputSourceRange<span class="token operator">:</span> process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span><span class="token punctuation">,</span>
        shouldDecodeNewlines<span class="token punctuation">,</span>
        shouldDecodeNewlinesForHref<span class="token punctuation">,</span>
        delimiters<span class="token operator">:</span> options<span class="token punctuation">.</span>delimiters<span class="token punctuation">,</span>
        comments<span class="token operator">:</span> options<span class="token punctuation">.</span>comments
      <span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token keyword">this</span><span class="token punctuation">)</span>
      options<span class="token punctuation">.</span>render <span class="token operator">=</span> render
      options<span class="token punctuation">.</span>staticRenderFns <span class="token operator">=</span> staticRenderFns

      <span class="token comment">/* istanbul ignore if */</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> config<span class="token punctuation">.</span>performance <span class="token operator">&amp;&amp;</span> mark<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">mark</span><span class="token punctuation">(</span><span class="token string">'compile end'</span><span class="token punctuation">)</span>
        <span class="token function">measure</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span><span class="token keyword">this</span><span class="token punctuation">.</span>_name<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> compile</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> <span class="token string">'compile'</span><span class="token punctuation">,</span> <span class="token string">'compile end'</span><span class="token punctuation">)</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">return</span> <span class="token function">mount</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> el<span class="token punctuation">,</span> hydrating<span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>阅读上面代码，我们能得到以下结论：</p> <ul><li><p>不要将根元素放到<code>body</code>或者<code>html</code>上</p></li> <li><p>可以在对象中定义<code>template/render</code>或者直接使用<code>template</code>、<code>el</code>表示元素选择器</p></li> <li><p>最终都会解析成<code>render</code>函数，调用<code>compileToFunctions</code>，会将<code>template</code>解析成<code>render</code>函数</p></li></ul> <p>对<code>template</code>的解析步骤大致分为以下几步：</p> <ul><li><p>将<code>html</code>文档片段解析成<code>ast</code>描述符</p></li> <li><p>将<code>ast</code>描述符解析成字符串</p></li> <li><p>生成<code>render</code>函数</p></li></ul> <p>生成<code>render</code>函数，挂载到<code>vm</code>上后，会再次调用<code>mount</code>方法</p> <p>源码位置：src\platforms\web\runtime\index.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token comment">// public mount method</span>
<span class="token class-name">Vue</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">$mount</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span>
  <span class="token parameter">el<span class="token operator">?</span><span class="token operator">:</span> string <span class="token operator">|</span> Element<span class="token punctuation">,</span>
  hydrating<span class="token operator">?</span><span class="token operator">:</span> boolean</span>
<span class="token punctuation">)</span><span class="token operator">:</span> Component <span class="token punctuation">{</span>
  el <span class="token operator">=</span> el <span class="token operator">&amp;&amp;</span> inBrowser <span class="token operator">?</span> <span class="token function">query</span><span class="token punctuation">(</span>el<span class="token punctuation">)</span> <span class="token operator">:</span> <span class="token keyword">undefined</span>
  <span class="token comment">// 渲染组件</span>
  <span class="token keyword">return</span> <span class="token function">mountComponent</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> el<span class="token punctuation">,</span> hydrating<span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>调用<code>mountComponent</code>渲染组件</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">mountComponent</span> <span class="token punctuation">(</span>
  <span class="token parameter">vm<span class="token operator">:</span> Component<span class="token punctuation">,</span>
  el<span class="token operator">:</span> <span class="token operator">?</span>Element<span class="token punctuation">,</span>
  hydrating<span class="token operator">?</span><span class="token operator">:</span> boolean</span>
<span class="token punctuation">)</span><span class="token operator">:</span> Component <span class="token punctuation">{</span>
  vm<span class="token punctuation">.</span>$el <span class="token operator">=</span> el
  <span class="token comment">// 如果没有获取解析的render函数，则会抛出警告</span>
  <span class="token comment">// render是解析模板文件生成的</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>render<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>render <span class="token operator">=</span> createEmptyVNode
    <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">/* istanbul ignore if */</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>template <span class="token operator">&amp;&amp;</span> vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>template<span class="token punctuation">.</span><span class="token function">charAt</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span> <span class="token operator">!==</span> <span class="token string">'#'</span><span class="token punctuation">)</span> <span class="token operator">||</span>
        vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>el <span class="token operator">||</span> el<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">warn</span><span class="token punctuation">(</span>
          <span class="token string">'You are using the runtime-only build of Vue where the template '</span> <span class="token operator">+</span>
          <span class="token string">'compiler is not available. Either pre-compile the templates into '</span> <span class="token operator">+</span>
          <span class="token string">'render functions, or use the compiler-included build.'</span><span class="token punctuation">,</span>
          vm
        <span class="token punctuation">)</span>
      <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
        <span class="token comment">// 没有获取到vue的模板文件</span>
        <span class="token function">warn</span><span class="token punctuation">(</span>
          <span class="token string">'Failed to mount component: template or render function not defined.'</span><span class="token punctuation">,</span>
          vm
        <span class="token punctuation">)</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
  <span class="token comment">// 执行beforeMount钩子</span>
  <span class="token function">callHook</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> <span class="token string">'beforeMount'</span><span class="token punctuation">)</span>

  <span class="token keyword">let</span> updateComponent
  <span class="token comment">/* istanbul ignore if */</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> config<span class="token punctuation">.</span>performance <span class="token operator">&amp;&amp;</span> mark<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function-variable function">updateComponent</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
      <span class="token keyword">const</span> name <span class="token operator">=</span> vm<span class="token punctuation">.</span>_name
      <span class="token keyword">const</span> id <span class="token operator">=</span> vm<span class="token punctuation">.</span>_uid
      <span class="token keyword">const</span> startTag <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue-perf-start:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>id<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span>
      <span class="token keyword">const</span> endTag <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue-perf-end:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>id<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span>

      <span class="token function">mark</span><span class="token punctuation">(</span>startTag<span class="token punctuation">)</span>
      <span class="token keyword">const</span> vnode <span class="token operator">=</span> vm<span class="token punctuation">.</span><span class="token function">_render</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
      <span class="token function">mark</span><span class="token punctuation">(</span>endTag<span class="token punctuation">)</span>
      <span class="token function">measure</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>name<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> render</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> startTag<span class="token punctuation">,</span> endTag<span class="token punctuation">)</span>

      <span class="token function">mark</span><span class="token punctuation">(</span>startTag<span class="token punctuation">)</span>
      vm<span class="token punctuation">.</span><span class="token function">_update</span><span class="token punctuation">(</span>vnode<span class="token punctuation">,</span> hydrating<span class="token punctuation">)</span>
      <span class="token function">mark</span><span class="token punctuation">(</span>endTag<span class="token punctuation">)</span>
      <span class="token function">measure</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">vue </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>name<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> patch</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> startTag<span class="token punctuation">,</span> endTag<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token comment">// 定义更新函数</span>
    <span class="token function-variable function">updateComponent</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
      <span class="token comment">// 实际调⽤是在lifeCycleMixin中定义的_update和renderMixin中定义的_render</span>
      vm<span class="token punctuation">.</span><span class="token function">_update</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span><span class="token function">_render</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> hydrating<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
  <span class="token comment">// we set this to vm._watcher inside the watcher's constructor</span>
  <span class="token comment">// since the watcher's initial patch may call $forceUpdate (e.g. inside child</span>
  <span class="token comment">// component's mounted hook), which relies on vm._watcher being already defined</span>
  <span class="token comment">// 监听当前组件状态，当有数据变化时，更新组件</span>
  <span class="token keyword">new</span> <span class="token class-name">Watcher</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> updateComponent<span class="token punctuation">,</span> noop<span class="token punctuation">,</span> <span class="token punctuation">{</span>
    <span class="token function">before</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span>vm<span class="token punctuation">.</span>_isMounted <span class="token operator">&amp;&amp;</span> <span class="token operator">!</span>vm<span class="token punctuation">.</span>_isDestroyed<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token comment">// 数据更新引发的组件更新</span>
        <span class="token function">callHook</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> <span class="token string">'beforeUpdate'</span><span class="token punctuation">)</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token boolean">true</span> <span class="token comment">/* isRenderWatcher */</span><span class="token punctuation">)</span>
  hydrating <span class="token operator">=</span> <span class="token boolean">false</span>

  <span class="token comment">// manually mounted instance, call mounted on self</span>
  <span class="token comment">// mounted is called for render-created child components in its inserted hook</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>vm<span class="token punctuation">.</span>$vnode <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    vm<span class="token punctuation">.</span>_isMounted <span class="token operator">=</span> <span class="token boolean">true</span>
    <span class="token function">callHook</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> <span class="token string">'mounted'</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">return</span> vm
<span class="token punctuation">}</span>
</code></pre></div><p>阅读上面代码，我们得到以下结论：</p> <ul><li>会触发<code>boforeCreate</code>钩子</li> <li>定义<code>updateComponent</code>渲染页面视图的方法</li> <li>监听组件数据，一旦发生变化，触发<code>beforeUpdate</code>生命钩子</li></ul> <p><code>updateComponent</code>方法主要执行在<code>vue</code>初始化时声明的<code>render</code>，<code>update</code>方法</p> <p><code>render</code>的作用主要是生成<code>vnode</code></p> <p>源码位置：src\core\instance\render.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token comment">// 定义vue 原型上的render方法</span>
<span class="token class-name">Vue</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">_render</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">:</span> VNode <span class="token punctuation">{</span>
    <span class="token keyword">const</span> vm<span class="token operator">:</span> Component <span class="token operator">=</span> <span class="token keyword">this</span>
    <span class="token comment">// render函数来自于组件的option</span>
    <span class="token keyword">const</span> <span class="token punctuation">{</span> render<span class="token punctuation">,</span> _parentVnode <span class="token punctuation">}</span> <span class="token operator">=</span> vm<span class="token punctuation">.</span>$options

    <span class="token keyword">if</span> <span class="token punctuation">(</span>_parentVnode<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        vm<span class="token punctuation">.</span>$scopedSlots <span class="token operator">=</span> <span class="token function">normalizeScopedSlots</span><span class="token punctuation">(</span>
            _parentVnode<span class="token punctuation">.</span>data<span class="token punctuation">.</span>scopedSlots<span class="token punctuation">,</span>
            vm<span class="token punctuation">.</span>$slots<span class="token punctuation">,</span>
            vm<span class="token punctuation">.</span>$scopedSlots
        <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">// set parent vnode. this allows render functions to have access</span>
    <span class="token comment">// to the data on the placeholder node.</span>
    vm<span class="token punctuation">.</span>$vnode <span class="token operator">=</span> _parentVnode
    <span class="token comment">// render self</span>
    <span class="token keyword">let</span> vnode
    <span class="token keyword">try</span> <span class="token punctuation">{</span>
        <span class="token comment">// There's no need to maintain a stack because all render fns are called</span>
        <span class="token comment">// separately from one another. Nested component's render fns are called</span>
        <span class="token comment">// when parent component is patched.</span>
        currentRenderingInstance <span class="token operator">=</span> vm
        <span class="token comment">// 调用render方法，自己的独特的render方法， 传入createElement参数，生成vNode</span>
        vnode <span class="token operator">=</span> <span class="token function">render</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span>_renderProxy<span class="token punctuation">,</span> vm<span class="token punctuation">.</span>$createElement<span class="token punctuation">)</span>
    <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">handleError</span><span class="token punctuation">(</span>e<span class="token punctuation">,</span> vm<span class="token punctuation">,</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">render</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
        <span class="token comment">// return error render result,</span>
        <span class="token comment">// or previous vnode to prevent render error causing blank component</span>
        <span class="token comment">/* istanbul ignore else */</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span>renderError<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">try</span> <span class="token punctuation">{</span>
                vnode <span class="token operator">=</span> vm<span class="token punctuation">.</span>$options<span class="token punctuation">.</span><span class="token function">renderError</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span>_renderProxy<span class="token punctuation">,</span> vm<span class="token punctuation">.</span>$createElement<span class="token punctuation">,</span> e<span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
                <span class="token function">handleError</span><span class="token punctuation">(</span>e<span class="token punctuation">,</span> vm<span class="token punctuation">,</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">renderError</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
                vnode <span class="token operator">=</span> vm<span class="token punctuation">.</span>_vnode
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
            vnode <span class="token operator">=</span> vm<span class="token punctuation">.</span>_vnode
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
        currentRenderingInstance <span class="token operator">=</span> <span class="token keyword">null</span>
    <span class="token punctuation">}</span>
    <span class="token comment">// if the returned array contains only a single node, allow it</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>vnode<span class="token punctuation">)</span> <span class="token operator">&amp;&amp;</span> vnode<span class="token punctuation">.</span>length <span class="token operator">===</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        vnode <span class="token operator">=</span> vnode<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span>
    <span class="token punctuation">}</span>
    <span class="token comment">// return empty vnode in case the render function errored out</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token punctuation">(</span>vnode <span class="token keyword">instanceof</span> <span class="token class-name">VNode</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>process<span class="token punctuation">.</span>env<span class="token punctuation">.</span><span class="token constant">NODE_ENV</span> <span class="token operator">!==</span> <span class="token string">'production'</span> <span class="token operator">&amp;&amp;</span> Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>vnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token function">warn</span><span class="token punctuation">(</span>
                <span class="token string">'Multiple root nodes returned from render function. Render function '</span> <span class="token operator">+</span>
                <span class="token string">'should return a single root node.'</span><span class="token punctuation">,</span>
                vm
            <span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        vnode <span class="token operator">=</span> <span class="token function">createEmptyVNode</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    <span class="token comment">// set parent</span>
    vnode<span class="token punctuation">.</span>parent <span class="token operator">=</span> _parentVnode
    <span class="token keyword">return</span> vnode
<span class="token punctuation">}</span>
</code></pre></div><p><code>_update</code>主要功能是调用<code>patch</code>，将<code>vnode</code>转换为真实<code>DOM</code>，并且更新到页面中</p> <p>源码位置：src\core\instance\lifecycle.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token class-name">Vue</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">_update</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">vnode<span class="token operator">:</span> VNode<span class="token punctuation">,</span> hydrating<span class="token operator">?</span><span class="token operator">:</span> boolean</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">const</span> vm<span class="token operator">:</span> Component <span class="token operator">=</span> <span class="token keyword">this</span>
    <span class="token keyword">const</span> prevEl <span class="token operator">=</span> vm<span class="token punctuation">.</span>$el
    <span class="token keyword">const</span> prevVnode <span class="token operator">=</span> vm<span class="token punctuation">.</span>_vnode
    <span class="token comment">// 设置当前激活的作用域</span>
    <span class="token keyword">const</span> restoreActiveInstance <span class="token operator">=</span> <span class="token function">setActiveInstance</span><span class="token punctuation">(</span>vm<span class="token punctuation">)</span>
    vm<span class="token punctuation">.</span>_vnode <span class="token operator">=</span> vnode
    <span class="token comment">// Vue.prototype.__patch__ is injected in entry points</span>
    <span class="token comment">// based on the rendering backend used.</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>prevVnode<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">// initial render</span>
      <span class="token comment">// 执行具体的挂载逻辑</span>
      vm<span class="token punctuation">.</span>$el <span class="token operator">=</span> vm<span class="token punctuation">.</span><span class="token function">__patch__</span><span class="token punctuation">(</span>vm<span class="token punctuation">.</span>$el<span class="token punctuation">,</span> vnode<span class="token punctuation">,</span> hydrating<span class="token punctuation">,</span> <span class="token boolean">false</span> <span class="token comment">/* removeOnly */</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
      <span class="token comment">// updates</span>
      vm<span class="token punctuation">.</span>$el <span class="token operator">=</span> vm<span class="token punctuation">.</span><span class="token function">__patch__</span><span class="token punctuation">(</span>prevVnode<span class="token punctuation">,</span> vnode<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    <span class="token function">restoreActiveInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
    <span class="token comment">// update __vue__ reference</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>prevEl<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      prevEl<span class="token punctuation">.</span>__vue__ <span class="token operator">=</span> <span class="token keyword">null</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>vm<span class="token punctuation">.</span>$el<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      vm<span class="token punctuation">.</span>$el<span class="token punctuation">.</span>__vue__ <span class="token operator">=</span> vm
    <span class="token punctuation">}</span>
    <span class="token comment">// if parent is an HOC, update its $el as well</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>vm<span class="token punctuation">.</span>$vnode <span class="token operator">&amp;&amp;</span> vm<span class="token punctuation">.</span>$parent <span class="token operator">&amp;&amp;</span> vm<span class="token punctuation">.</span>$vnode <span class="token operator">===</span> vm<span class="token punctuation">.</span>$parent<span class="token punctuation">.</span>_vnode<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      vm<span class="token punctuation">.</span>$parent<span class="token punctuation">.</span>$el <span class="token operator">=</span> vm<span class="token punctuation">.</span>$el
    <span class="token punctuation">}</span>
    <span class="token comment">// updated hook is called by the scheduler to ensure that children are</span>
    <span class="token comment">// updated in a parent's updated hook.</span>
  <span class="token punctuation">}</span>
</code></pre></div><h2 id="三、结论"><a href="#三、结论" class="header-anchor">#</a> 三、结论</h2> <ul><li><p><code>new Vue</code>的时候调用会调用<code>_init</code>方法</p> <ul><li>定义 <code>$set</code>、<code>$get</code> 、<code>$delete</code>、<code>$watch</code> 等方法</li> <li>定义 <code>$on</code>、<code>$off</code>、<code>$emit</code>、<code>$off</code>等事件</li> <li>定义 <code>_update</code>、<code>$forceUpdate</code>、<code>$destroy</code>生命周期</li></ul></li> <li><p>调用<code>$mount</code>进行页面的挂载</p></li> <li><p>挂载的时候主要是通过<code>mountComponent</code>方法</p></li> <li><p>定义<code>updateComponent</code>更新函数</p></li> <li><p>执行<code>render</code>生成虚拟<code>DOM</code></p></li> <li><p><code>_update</code>将虚拟<code>DOM</code>生成真实<code>DOM</code>结构，并且渲染到页面中</p></li></ul> <h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li>https://www.cnblogs.com/gerry2019/p/12001661.html</li> <li>https://github.com/vuejs/vue/tree/dev/src/core/instance</li> <li>https://vue3js.cn</li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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